12,614 research outputs found
Topological surface states and Fermi arcs of the noncentrosymmetric Weyl semimetals TaAs, TaP, NbAs, and NbP
Very recently the topological Weyl semimetal (WSM) state was predicted in the
noncentrosymmetric compounds TaAs, TaP, NbAs, and NbP and soon led to
photoemission and transport experiments to verify the presumed topological
properties such as Fermi arcs (unclosed Fermi surfaces) and the chiral anomaly.
In this work, we have performed fully \textit{ab initio} calculations of the
surface band structures of these four WSM materials and revealed the Fermi arcs
with spin-momentum-locked spin texture. On the (001) polar surface, the shape
of the Fermi surface depends sensitively on the surface terminations (cations
or anions), although they exhibit the same topology with arcs. The anion (P or
As) terminated surfaces are found to fit recent photoemission measurements
well. Such surface potential dependence indicates that the shape of the Fermi
surface can be manipulated by depositing guest species (such as K atoms), as we
demonstrate. On the polar surface of a WSM without inversion symmetry,
Rashba-type spin polarization naturally exists in the surface states and leads
to strong spin texture. By tracing the spin polarization of the Fermi surface,
we can also distinguish Fermi arcs from trivial Fermi circles. The four
compounds NbP, NbAs, TaP, and TaAs present an increasing amplitude of
spin-orbit coupling (SOC) in the band structure. By comparing their surface
states, we reveal the evolution of topological Fermi arcs from the
spin-degenerate Fermi circle to spin-split arcs when the SOC increases from
zero to a finite value. Our work will help us understand the complicated
surface states of WSMs and allow us to manipulate them, especially for future
spin-revolved photoemission and transport experiments.Comment: This manuscript has been submitted to Physical Review B on 22 Jul.
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Electron beams of cylindrically symmetric spin polarization
Cylindrically symmetric electron beams in spin polarization are reported for
the first time. They are shown to be the eigen states of total angular momentum
in the direction. But they are neither the eigen states of spin nor the
eigen states of orbital angular momentum in that direction.Comment: 10 pages and 2 figure
Hidden type-II Weyl points in the Weyl semimetal NbP
As one of Weyl semimetals discovered recently, NbP exhibits two groups of
Weyl points with one group lying inside the plane and the other group
staying away from this plane. All Weyl points have been assumed to be type-I,
for which the Fermi surface shrinks into a point as the Fermi energy crosses
the Weyl point. In this work, we have revealed that the second group of Weyl
points are actually type-II, which are found to be touching points between the
electron and hole pockets in the Fermi surface. Corresponding Weyl cones are
strongly tilted along a line approximately off the axis in the
(or ) plane, violating the Lorentz symmetry but still
giving rise to Fermi arcs on the surface. Therefore, NbP exhibits both type-I
( plane) and type-II ( plane) Weyl points.Comment: 5 pages and 4 figure
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